In many modern electronics applications, it is needed to convert an analog value to a digital value. For example, it some applications it can be needed to convert a continuous physical quantity (such as a voltage) to digital value that represents the amplitude of the physical quantity. Analog-to-digital converters (ADC's) are electronic devices that can be implemented to provide such conversions.
One issue in ADCs is the need for conversion of weakly driven signals. In general, weakly driven signals are those with relatively large source impedance (e.g., a source impedance of greater than 1 Mega ohm). A signal having such a relatively large source impedance can have a temporarily drop in voltage with even a moderate current flow. This temporary drop of the voltage can cause a variety of unwanted effects on its associated system.
For example, in one application the weakly driven signal is a reference signal used to provide a reference voltage during operation of the device. When such a weakly driven reference signal is measured by a traditional ADC, the voltage of the reference signal can temporarily drop below a critical level. This temporary drop of the reference signal below the critical level can have a variety of unwanted effects. For example, in some applications the temporary drop in voltage of the reference signal may cause a system reset or other unwanted event.
Unfortunately, current techniques for analog-to-digital conversion can lack the ability to accurately measure weakly driven signals without causing such a temporary voltage drop and resulting unwanted events. Thus, what are needed are improved devices and techniques for the analog-to-digital conversion of weakly driven signals that can reduce the likelihood of excessive voltage drop during analog-to-digital conversion.